1. Field of the Invention
The present invention relates to a skeletal implant, and more particularly to an implant of this type to be used for connecting at least two elements of the skeleton, which implant is embodied in at least two parts, each of which is capable of being connected to one of these elements.
According to a first aspect of the invention, it relates to a consolidating and/or connecting implant, and more particularly to an implant of this type to be used to consolidate a connection between two bone elements, of the type comprising a first part designed to be attached to one of the elements and a second part designed to be attached to the other element.
2. Background and Material Information
There are known implants of this type that are capable of being used, for example, in the case of a performance of a bone graft or during the formation of a callus following a fracture. The two ends of the implant, which are rigidly connected to one another, for example because they are embodied in one piece, are each attached, for example screwed, to a bone element located on either side of the graft. When the graft has consolidated, the implant can be removed.
However, there are numerous cases where the implant is left in place. This is particularly the case when the implant is used to replace a bone structure which is impossible to restore or to construct.
In such cases, the rigidity of the implant, which is often indispensable at the beginning of the implantation, during the formation of the callus, later constitutes a drawback. In effect, the bone structures no longer sustain sufficient mechanical stress. Therefore, they do not reconstitute themselves in an optimal way, this reconstitution being tied to a satisfactory stressing of the bone, the disturbance of which has consequences which can result in post-surgical pain that is very difficult to treat.
Moreover, when the implant is to be used to connect two bone elements which are normally capable of moving relative to one another, as in the case of a rachidian implant, this rigidity results in a functional handicap in the patient in whom it is implanted, and excessive stress on the neighboring joints.
The object of the invention is, among other things, to eliminate these drawbacks.
According to a second aspect of the invention, it relates to an articulated implant, and more particularly to an implant of this type intended either to be intercalated between two bone elements in relative motion, such as an artificial intervertebral disk, or to replace a joint or an element of a joint, such as an artificial head of the femur.
As regards the intercalated implant, it can be beneficial to assist the adjacent bone structures and the ligaments during rapid, or even violent movements. On the other hand, it may be preferable to allow these structures and ligaments to work during slow movements or simple static loads in order to prevent atrophy or weakening.
As regards the articulated implant itself, a completely rigid structure fully transmits the shocks and vibrations to the other element of the joint, resulting in a risk of dystrophy or rupture of this other element.
Also, once a surgical skeleton implant is implanted no modification can be made to adapt the implant to the changing needs of the patients.
Another object of the present invention is to eliminate these drawbacks.
To this end, the subject of the invention is a skeletal implant of the type to be used for connecting at least two elements of the skeleton, which implant is embodied in at least two parts, each of which is capable of being connected to one of these elements, there parts being movable with respect to each other, characterized in that it comprises between these two parts at least one adjustable device responsive to non invasive control means, said control means being preferably located on said implant, to exert an adjustable force, for example a distraction or compression force, between said parts, and/or to authorise an adjustable displacement between said parts between a starting position and a displaced position in which said parts should, at least temporarily, be maintained, and/or to secure a damping effect with an adjustable coefficient of resistance.
It is noted, first of all, that the adjustment can be discrete as well as continuous, and for example, can include only two positions of adjustment.
It is known that a shock-absorbing device is a device generally comprising two chambers of variable volume filled with a hydraulic fluid and connected by a calibrated opening. A device of this type is intended to  less than  less than cushion greater than  greater than  the movements between two elements, one of which is connected to a structure of one of the chambers, the other being connected to an element in which the calibrated opening is formed.
When the two elements move relative to one another, the volumes of the two chambers vary in inverse proportion to one another, the hydraulic fluid being laminated at the level of the calibrated opening. The result is a force which opposes the relative movement between the two elements which, as will be shown, is proportional to the speed of this movement.
Used within the scope of the invention, a device of this type applied to an implant of the consolidating and/or connecting type has the advantage of allowing the bone structures to function, and thus to develop, in a practically normal way at moderate relative speeds between the bone elements connected by the implant, particularly in the case of static stresses. On the other hand, the greater the relative speeds, particularly in the case of voluntary rapid movement or shock, that is, dynamic stresses, the greater the portion of the stress absorbed by the implant.
The result is that the osteo-ligamentous structure, weakened by the situation which justified the insertion of the implant, can nevertheless function and thus reconstitute normally as long as the stresses remain moderate. But the greater these stresses, the more the natural structure is assisted by the implant.
Moreover, the coefficient of resistance being adjustable, it is possible to reduce it progressively as the bone structure reconstitutes. The latter can also sustain more and more dynamic stresses until, eventually, it returns to normal functioning.
It is noted that it has already been suggested in the prior art to endow prostheses with viscous and/or elastic means intended to absorb shocks. Likewise, it is well known to provide, in certain prostheses, regulating or adjusting means. However, no prosthesis with a functional characteristic of viscous resistance has yet been proposed wherein the coefficient of resistance would be adjustable. This combination is essential in the primary function of the invention, which is to allow a progressive reconstitution of the bone structure and an optimal continuous adaptation to the state of this structure.
When applied to an articulated implant, the invention also makes it possible to give the articulation greater flexibility, which, as in the prior art, allows it to absorb shocks, but in this case also allows the neighboring bone structures and ligaments to work.
Finally, the consequence of this shock-absorbing characteristic is to protect the implant itself, as well as joints located above and below the implant, from shocks.
In one particular embodiment, the implant comprises removable means for locking the shock-absorbing device at a predetermined length.
The implant according to the invention, in this embodiment, can function during a first period in the traditional way, like a rigid implant. This phase of functioning is for example that of the formation of the callus in the case of a graft. During a second period, the locking means are removed and the implant functions according to the invention, exerting between the elements to which it is connected a force which is proportional to their relative speed and is therefore a function of the stresses exerted in the graft.
In another particular embodiment, the implant comprises means for limiting the travel of the shock-absorbing device.
This has the advantage of rendering the implant rigid in the case where the stresses reach a certain limit. Thus, there is no risk of reaching the rupture stress point.
Advantageously, these means for limiting the travel are adjustable.
The travel of the shock-absorbing device can therefore be adapted to the patient and possibly increased progressively as the graft strengthens.
An implant according to the invention can be embodied in the form of an elongated element such as a screw, or a pin such as a coxofemoral prosthesis pin, or even the neck, the body or the head of a femoral prosthesis, comprising two end parts connected by a flexible middle part, the middle part comprising two chambers filled with hydraulic fluid, disposed on either side of a neutral axis and designed such that one of them increases in volume while the other decreases in volume when the implant flexes, these chambers being linked by at least one calibrated conduit.
This embodiment can be used to connect the two parts of a fractured bone to one another, for example the femur at the level of the neck or the diaphysis. The screw is positioned so that its middle part is located at the point of the fracture, with its neutral axis disposed as near as possible to the plane of maximum flexion under stress. Thus, after the formation of the callus, the implant will continue to assist it during sudden efforts, the hydraulic fluid being forced from the chamber whose volume decreases to the chamber whose volume increases, through the calibrated opening. On the other hand, the callus will sustain the static stresses on its own.
More particularly, these end parts can be connected by an elastic wall delimiting these chambers with a peripheral bellows.
As will be seen below, it is often advantageous to add an elastic component to the viscous component of the implant""s behavior.
The calibrated conduit can be embodied in the form of borings in at least one of the end parts.
This produces a very compact embodiment that is well suited to the embodiments of the implant in the form of a screw.
Advantageously, a valve is provided on the calibrated conduit.
This valve can initially be closed during the formation of the callus. Thus the implant is perfectly rigid and behaves like a classic screw. The valve is then opened so that the implant functions according to the invention, with its shock-absorbing function. A valve with a progressive opening also makes it possible to provide the function for adjusting the coefficient of resistance.
The control of the valve is preferably housed at the end of the implant, nearest the skin.
Thus, a completely non-invasive intervention allows the valve to be opened and possibly adjusted.
In a particular embodiment which is especially well suited to the performance of a bone graft for the purpose of replacing an injured vertebra, the shock-absorbing device comprises at least one chamber formed of two semi-chambers joined by a bellows, each of the semi-chambers being connected to one of the parts of the implant, this chamber being filled with a hydraulic fluid, and at least one calibrated opening being provided in a wall of this chamber for connecting this chamber with another chamber.
This disposition has the advantage of being very compact and preventing the relative slippage of the mechanical parts, with the resulting risk of hydraulic fluid leakage. However, in certain cases a traditional cylinder-and-piston shock-absorber may be preferred.
More particularly, these semi-chambers can be in the form of cupels whose openings face one another.
The above-mentioned locking means can in this case comprise a removable elongated locking element, inserted into a fold of the bellows so as to prevent it from collapsing.
The elongated locking element can be embodied in any appropriate way, for example in the form of a metal beaded chain.
The above-mentioned means for limiting the travel can comprise a stop ring screwed onto one of the semi-chambers and designed to cooperate with a shoulder of the other semi-chamber to prevent the two semi-chambers from moving toward one another beyond a certain limit.
The other chamber can be housed in a supporting skirt mounted on one of the semi-chambers around the calibrated opening, opposite the other semi chamber.
This other chamber can also be formed of two semi-chambers joined by a bellows.
In a preferred embodiment, the implant according to the invention also includes elastic means between these two parts.
In effect, it is often beneficial for the resistance to the relative displacement of the two parts of the implant to be proportional not only to the speed of this displacement, but also to the value of this displacement itself relative to a nominal position. Thus, the implant""s assistance to the surrounding bone structures is even more efficient when they are farther apart than in their normal configuration.
Advantageously, the coefficient of elasticity is adjustable.
Thus, it is possible to adjust the elasticity of the implant and, for example, to render it increasingly flexible as the surrounding structure re-establish themselves.
This type of elasticity can be obtained in an implant comprising two chambers filled with hydraulic fluid and joined by a calibrated opening, at least one of which chambers contains a compression ampulla at ambient pressure with elastic walls.
When a movement between the two parts of the implant begins, it produces a pressure variation in the chambers, and thus an elastic reaction of the compressible ampulla.
The wall of this ampulla can have progressive elasticity, one of the chambers being capable of being joined to a source of fluid under pressure.
Thus, in this case, it is possible to regulate the elasticity of the implant by adjusting the pressure in the cambers.
Means can be provided for adjusting the cross section of the calibrated opening.
In particular, these means for adjusting the cross section of the calibrated opening can comprise a hydraulically controlled needle valve.
Another subject of the present invention is an implant of the type described above wherein the shock-absorbing device comprises at least two chambers, specifically two low-pressure chambers whose wails are made of elastic material, these chambers being jointed by at least one calibrated conduit and filled with hydraulic fluid, and designed to sustain a differential pressure variation during a relative movement of the elements.
This type of design makes it possible to easily obtain implants which, as above, not only have a viscous resistance which is a function of the speed, but also an elastic resistance which is a function of the displacement.
In this case, the cross-section of the conduit can advantageously be determined by the prevailing pressure in a high-pressure chamber which is capable of compressing this conduit.
As a result of this design, the coefficient of resistance of the implant can be regulated very easily by adjusting the pressure in the high-pressure chamber.
In particular, one of the low-pressure chambers can have a wall of relatively low rigidity relative to the rigidity of the walls of the other chamber.
This design allows the implant to function even when the two chambers are not stressed differently. During a movement which creates excessive pressure, the pressure increases more in the rigid-walled chamber, resulting in a flow of the hydraulic fluid from this chamber to the chamber with the less rigid wall, and thus a shock-absorbing effect.
In one particular embodiment, a high-pressure chamber and a low-pressure chamber can be connected, in the low-pressure to high-pressure direction, by a non-return valve.
As will be seen, this disposition makes it possible to increase the pressure difference between the high-pressure and low-pressure chambers. It also makes it possible to maintain this difference despite possible leaks in the high-pressure to low-pressure direction.
The anti-return valve can comprise a flexible tube connected to the low-pressure chamber, one free end of which is inserted into a free end of a tube connected to the high-pressure chamber.
This type of valve is very small and also has the advantage of being even more tightly closed when the pressure difference is greater.
Preferably, it is also arranged for these chambers to be connected by a pressure regulation valve in parallel with the anti-return valve.
It will be seen that the anti-return valve is preferably disposed between the high-rigidity, low-pressure chamber and the high-pressure chamber.
In one particular embodiment, the implant according to the invention comprises a first annular low-pressure chamber, and a second rotating chamber in the center of the first chamber, the calibrated conduits being formed radially in the wall separating the two chambers.
Advantageously, the outer wall of the first low-pressure chamber is relatively thin, and the wall separating the two low-pressure chambers if relatively thick.
This implant can comprise at least one annular high-pressure chamber formed within the thickness of the wall separating the two low-pressure chambers, and designed to compress the calibrated conduits.
In another embodiment, this conduit is at least partially embodied in the form of a tube of elastic material surrounded by a tube that is substantially more rigid, these tubes being joined into rings at their ends, the compressed volume between the two tubes forming a high-pressure chamber.
In another particular embodiment, the implant is substantially disk-shaped, comprising a plurality of low-pressure chambers in sectors, joined by the calibrated conduits, which alternate inside the thickness of the disk with the high-pressure chambers.
Advantageously, the implant according to the invention comprises means for adjusting the distance between the elements it connects.
This type of design makes it possible, in particular, to alleviate possible post-operative pain by adjusting this distance appropriately. It is also particularly advantageous in the case of prostheses intended for children who are still growing.
These adjusting means can comprise a bellows designed to receive a hydraulic fluid, and means for connecting this bellows to a source of fluid under pressure.
Another subject of the invention is a pair of implants as described above, the low-pressure chamber of each of the implants being connected by the anti-return valve to the high-pressure chamber of the other implant.
A pair of implants of this type can particularly be provided, in the case of a graft of the vertebral column, to assist the graft in case of lateral flexion.
More generally, a pair of implants according to the invention can include means for automatically adapting to the movements of the wearer of the implants.
Up to this point, bone consolidation implants embodied according to the invention have been described. It will now be shown that the invention is also well suited to the embodiment of articulated implants.
In this case, each part of an implant as described above is articulated to the other.
More particularly, these parts can have complementary surfaces which rest against one anther, forming a ball-and-socket joint.
An articulated implant of this type can include, in particular, a pivot integral with one of the parts and housed in a space formed between a plurality of low-pressure chambers in the form of sections, which are integral with the other part of the implant and joined by the calibrated conduits, which themselves alternate with high-pressure chambers.
These embodiments are suitable as intervertebral disks.
In a particular application to a coxofemoral joint, the implant according to the invention comprises an articulating hollow sphere whose wall is open so as to allow the insertion of the end of a connecting pin, the shock-absorbing device being disposed inside this sphere between the wall of the latter and the end of the connecting pin.
More particularly, this shock-absorbing device can comprise an end element of the connecting pin designed to slide through a slot of a partition inside the sphere, which partition delimits two chambers in the sphere, and at least one calibrated opening is formed inside this end element between the two chambers.
In another embodiment, this shock-absorbing device can include an end element of the connecting pin disposed between two shock-absorbing elements, each of which includes at least two low-pressure chambers whose walls are made of elastic material, these chambers being connected by at least one calibrated conduit and filled with hydraulic fluid, and designed to sustain a differential pressure variation during a relative movement of the sphere and the connecting pin.
Another subject of the invention is a pair of implants as described above, used particularly within the scope of an arthrodesis of the vertebral column, each of the implants being mechanically connected in series to a connecting pin of a known type.
More particularly, each of the implants can include means for adjusting the distance between the two elements it connects.
It is thus possible, using a pair of implants of this type, not only to perform the arthrodesis, but also to adjust the angle and the distance between the two parts of the vertebral column connected by the prosthesis.
In one particular mode of embodiment, these adjusting means include, for each implant, an expandable element such as a bellows, designed to receive a hydraulic fluid, and means for connecting this bellows to a source of fluid under pressure.
This source of fluid under pressure can comprise a high-pressure fluid reservoir.
Advantageously, this high-pressure reservoir is common to both implants, each expandable element is also connected to a low-pressure reservoir, and an expandable refill cell is mechanically connected in series to each pin, each refill cell being connected to the high-pressure and low-pressure reservoirs by two anti-return valves, one of which allows a flow of fluid from the low-pressure reservoir to the refill cell, the other allowing a flow of fluid from the refill cell to the high-pressure reservoir.
It will be seen that this type of design makes it possible to produce a pump activated by the movements of the wearer of the implants.
In another particular embodiment, the above-mentioned pair of implants if formed of implants in which the shock-absorbing device comprises at least two chambers, these chambers being connected by at least one calibrated conduit and filled with hydraulic fluid, and designed to sustain a differential pressure variation during a relative movement of these elements, the cross-section of this calibrated conduit being determined by the prevailing pressure in a high-pressure chamber, and the high-pressure chambers of the implants are connected to the high-pressure reservoir by a controllable valve.
Another subject of the invention is a skeletal implant as described above, specifically belonging to a pair of implants, which includes sensors of physical quantities, including pressure, supplied with electric power and controlled from outside the body in a non-invasive way, and designed to transmit their information to display means.
More particularly, this implant can also include adjusting actuators which are also supplied with electric power and controlled from outside the body in a non-invasive way.
In facts the implants which were described have a variable length or dimension, the two parts or ends of the implant being able to move apart from one another or approach one another actively and/or passively, for example along the longitudinal axis of the implant, by virtue of the interposition of a deformable element, for example a hydraulic element, control means and/or regulating means being provided so as to make it possible to obtain a change in dimension of the implant in order to modify the distance between the two bone elements and/or to ensure an adjustable viscous or viscoelastic damping permitting a slow movement between the two bone elements and also counteracting a more abrupt displacement.
If necessary, a sufficiently high hydraulic pressure can be maintained by using the effect of a mechanical pump, actuated by the movements of the body, with a pressure-limiting valve flap, cooperating with a low-pressure reservoir.
For example, double implants consisting of two individual implants can be disposed respectively on either side of the spine in order to connect two vertebrae, each of the two elements thus being fixed to a lower vertebra via an anchoring means, such as a pedicle screw, and to an upper vertebra, either adjacent or more distant, likewise each time by an anchoring means, such as a pedicle screw.
In the case of a double implant consisting of two individual implants acting on the same skeletal structures, the two individual implants hydraulically can be interconnected in such a way as to permit pivoting movements of the bone elements relative to one another, namely a lateral pivoting in the frontal plane of the spine, by increasing the length of one of the individual implants and concomitantly reducing the length of the other implant, for a correction of deformation and/or a damping of lateral flexion.
By virtue of control means, for example noninvasive means of the magnetic type, it is possible to effect the desired modifications to the dimension of the individual implants and/or the modifications to the damping coefficient of the element acting as a damper. Moreover, means can be provided for automatically modifying the damping coefficient or the viscosity as a function of the movements of the body.
In brief, the present invention proposes realizing and perfecting an implantable device comprising at least one implant equipped with two end parts which can be fixed, by anchoring means, on at least two elements or parts of the skeleton, and comprising means of displacement, preferably at least partially reversible, between the said two ends, these means being arranged to provoke and/or maintain a displacement between the said elements of the skeleton.
This displacement can be a rectilinear and/or curved displacement, for example it can be a displacement of elongation, also called distraction, or a displacement of shortening, called compression, or a displacement in rotation, it being possible for this rotation to be isolated or, on the contrary, to be combined with a distraction or a compression.
In the simplest embodiment, in which the said displacement means are capable of maintaining but not provoking the displacement, these displacement means are controlled by control means, preferably noninvasive ones, which make it possible to release them so as to allow the patient, or another party, to modify the relative position of the two portions or elements of the skeleton, after which the said control means are actuated in order to block the implant in this new position, an inverse or reversible displacement still remaining possible if one acts once more on the control means, for example in the case where the displacements would have been too great.
In another preferred embodiment of the invention, the said displacement means include a motor means with which it is possible to impose a displacement between the said ends by exerting a force between them.
In a particular embodiment, this force can be exerted temporarily, that is to say for quite a brief instant, far the purpose of provoking a therapeutically desirable displacement between the two portions or elements of the skeleton, such a displacement often being intended for a small amplitude, since it is rapidly impeded by the anatomical structures which must not be traumatized. At the end of this instant, the control means make it possible to block the two ends relative to one another and to maintain the implant in its new position.
In another embodiment, by contrast, the said displacement means are capable of exerting an anatomically active permanent force between the said two ends, it being possible for this force to be constant or variable in such a way as to exert on the anatomical environment a stress which will gradually permit an anatomically desired displacement between the said two portions or elements of the skeleton, these motor means being controllable by control means with which it is possible to permit or interrupt their functioning and/or to adjust the intensity of the force.
If appropriate, the implant can also include viscous or viscoelastic damping means which can be used when the implant is blocked in its dimension or when the implant is freed or when it exerts its permanent active force. Such means have been described in the abovementioned European and American applications.
The said means of displacement and, if necessary, the said motor means can be of the hydraulic and/or mechanical and/or electrical type, a hydraulic type being preferred.
In one embodiment using hydraulic means, the implant preferably includes: two parts or end elements, for example rods, each receiving at least one means for anchoring in a skeletal part; at least one deformable element, preferably hydraulic, interposed between the said two elements, and permitting a variation in dimension and/or the creation of an active force between them; preferably at least one high-pressure reservoir, called a reserve, with which it is possible to address the high pressure, on demand, to a functional user circuit; preferably at least one low-pressure collection reservoir connected to the high-pressure reservoir via a pressure control valve; preferably at least one circuit for recharging the high-pressure reservoir, comprising at least one deformable element, preferably sensitive to physical positions or movements of the body receiving the implant; to generate a high pressure which, if so required, feeds the high-pressure reservoir; at least one functional circuit, namely: a circuit for modifying the dimension, for example the length, of the implant, comprising the said deformable element with which it is possible to modify a dimension between the two end elements and/or to establish, between the two end elements, an active force capable of provoking a progressive modification of the dimension between the said end elements, the said deformable element being connected on the one hand to the high-pressure reserve reservoir by way of a first valve and, on the other hand, to the low-pressure collection reservoir by way of a second valve in order to make it possible, as a function of the control of the said valves, to increase and/or reduce the dimension of the said deformable element in order to permit or provoke a lasting modification to the said dimension of the said individual implant, and/or a viscous or viscoelastic damping circuit comprising: if appropriate, an elastic element surgically interposed between the said two end elements of the implant, and a hydraulic damping element comprising at least one deformable element sensitive to the speed of a dimensional variation of the implant and communicating with a discharge reservoir by way of a throttle means, and control means which can preferably be actuated from outside the body of the patient, in order to modify the dimension of the implant and/or the force exerted by the implant and/or the damping properties.
Of course, one and the same piece, for example a deformable element, can form a constituent part of several of the constituents defined hereinabove.
The circuit for recharging the high-pressure reservoir is in fact intended to act as a very high-pressure pump, making it possible to establish and to maintain a high pressure in a high-pressure reservoir
Preferably, especially in the preferred case where the deformable element of the high-pressure recharging circuit is sensitive to physical positions or movements of the patient receiving the implant, this deformable element has a small surface compared with the active surface of the element which transmits to it the force originating from the body, in such a way as to ensure a pressure-multiplying differential effect, it being understood that upon each stress only a small quantity of very high-pressure fluid is sent towards the high-pressure chamber.
The deformable element of the circuit for recharging the high-pressure reservoir can also be actuated by external means while remaining implanted. Thus, for example, this deformable element can be in the form of a pump, preferably formed by a metal bellows, implanted on a part of the body at a point where an external pressure can be applied to it, for example implanted on the posterior face of the sacrum, allowing this pump or bellows to be actuated by hand via the external anatomical planes.
Alternatively, this pump could be of the magnetic or electromagnetic type, having, for example, a movable core actuating a small piston or bellows under the influence of an electromagnetic force of external origin.
It will also be appreciated that the present application incorporates the alternatives and equivalents using non-hydraulic motor and/or damping means, ensuring the same functions of lasting and adjustable modification of dimension and/or force and/or adjustable modification or variation of the damping coefficient.
Solely by way of example, an implant of the uniquely mechanical type can comprise a first end, movable in translation relative to the second end, and secured to a rod which is immobilized by a catch which is sensitive to an external magnetic control means for blocking or releasing the said rod, a motor means being interposed between the said rod and the said second end, it being possible for this motor means to be in the form of a spring or another precharged elastic element tending to displace one of the ends relative to the other when the catch is released, it being possible for the movement to be reversible, at least once, for example by inserting, between the spring and the said second end, a spring support piece which can be displaced, by virtue of other magnetic control means, in such away as to at least partially relax the spring. Alternatively, the implant can include several springs arranged in parallel and capable of being used separately by release means which are sensitive to control means.
In another embodiment, an implant can include displacement means of the electromagnetic type, for example a solenoid with a plunger core, the solenoid being secured to one of the ends of an implant and the plunger core being secured to the other end, blocking means preferably being provided for immobilizing the core relative to the solenoid in at least two different positions, the solenoid being capable of being powered, via a control means, from an electrical energy source, for example an implanted battery and/or an accumulator which can be recharged by antenna transmission with transcutaneous coupling.
Such embodiments are reversible within the meaning of the invention because, if so desired, they permit a modification in the opposite direction, at least partially, of the dimensional modification which has been established.
The present invention also makes it possible to perfect the movements or forces of rotation permitted or imposed by an implant or a set of at least two individual implants in the frontal and/or sagittal and/or horizontal plane.
For example, the invention can provide implants of this type with which it is possible to impose symmetrical movements of rotation, that is to say in the same direction and of the same value of rotation, of the pedicle screws or similar anchoring means of the two individual implant parts, or, by contrast, antisymmetrical movements, that is to say in opposite directions, or else independent of one another.
Generally speaking, the movement or force of rotation controlled between the two anchoring means of an implant according to the invention and, where appropriate, the coordination of the movements or forces of rotation of the anchoring means of several implants, for example the individual implants of a double implant, will make it possible, depending on requirements, to approximate much more closely the theoretically possible or desirable natural movement between the two bone parts to which the anchoring means are fixed, so as to impose progressive displacements, for example for corrections, and/or progressively modifiable damping, ranging, for example, from rigidity during a phase of bone consolidation or healing to progressive mobility, making it possible, for example, to safeguard a joint.
The skeletal implant has a first and a second part or end element, means for anchoring in bone parts, which means are connected respectively to the said first and second end elements, at least one deformable element connected respectively to the said first and second anchoring means, and means permitting a nonrectilinear movement, particularly a rotation, between the said anchoring means.
The implant can include means permitting a rotation between the said end elements.
The said deformable element can be deformable in rotation.
The implant can include means permitting a rotation of at least one of the said anchoring means relative to the end piece to which it is connected.
The abovementioned movement of rotation can also be combined with movements of translation, in such a way that the resulting movement can be a complex nonrectilinear displacement.
According to one refinement, the skeletal implant, having a first and a second end element, means for anchoring in bone parts, for example by way of screws, such as, for example, pedicle screws situated at the said ends, at least one deformable element, for example a hydraulic element, containing an incompressible hydraulic fluid and interposed between the two end elements, and means for actuating the deformable element, for example, if necessary, hydraulic circuit means connected to the said at least one deformable element interposed between the said ends, and capable of permitting a lasting modification, preferably obtained progressively, of the distance or the force between the said two ends and/or a viscoelastic damping of the movements between the said two ends, the said actuating means, for example the said hydraulic circuit means, being sensitive to control means which can preferably be actuated from outside the body of the patient, is characterized in that the said fixing or anchoring means are fixed to the said two ends by articulated attachment means, and in that the said fixing or anchoring means are additionally connected to one another via a rigid joining element which is relatively parallel to the geometric axis connecting the said two ends of the implant and is situated at a certain distance from the said axis, by attachment means which are likewise articulated, for example in such a way as to form between the said four attachment points a deformable quadrilateral, permitting an angular movement of rotation of the said fixing or anchoring means relative to one another.
These articulated attachment means can consist of actual mechanical articulations or of suitably deformable joining means.
For example, the articulations can be articulations using a ball which is received rotatably in a seat of the end piece, this ball having a passage through which it can receive and hold a part of an anchoring means, such as a pedicle screw. Of course, all other articulation principles such as a pivot articulation can be used.
In one embodiment, the said joining element is situated between the axis of the implant and the bone elements to which the implant is fixed, but in another embodiment the said joining element is arranged on the other side of the axis of the implant in relation to the bone elements which are joined by the implant.
The said joining elements can be simple rigid links such as rods or bars of invariable length.
However, in another embodiment, these joining elements themselves can include, between their ends, at least one deformable zone, which then makes it possible to effect displacements, such as, for example, an elongation of the implant without relative rotation of the fixing means, by simultaneous modification of the length of the actual element and of the joining element, and/or to effect a viscoelastic damping between the bone elements without any movement of rotation of the said fixing means.
A complex implant in accordance with the invention can be formed by using two individual implants arranged, for example, side by side, for example on either side of the spinous processes of the vertebral column, with a hydraulic interconnection making it possible to effect at least one of the following functions: antisymmetrical rotation movement of the means of one individual implant relative to the movement of the anchoring means of the other implant, symmetrical movements of the said anchoring means, independent movements.
Of course, for the sake of simplicity, the two individual elements of a complex implant can use common hydraulic elements, such as, for example, high-pressure reservoir, low-pressure collector, means for creating the high pressure, and means for controlling the hydraulic circuit.
In another embodiment, intended to permit a rotation in a transverse plane, or, if appropriate, an oblique plane, relative to the general direction of the implant, that is to say the direction connecting the two anchoring means or screws, the skeletal implant, having a first and a second end element, means for fixing or anchoring in bone parts, for example by way of screws, for example pedicle screws situated at the ends, at least one deformable element interposed between the two end elements, and its actuating means, to permit a lasting modification, preferably obtained progressively, of the distance between one end and an element movable relative to the said one end, and control means, which can preferably be actuated from outside the body of the patient, is characterized in that the said movable element is arranged to provoke or permit a rotation of the other of the two ends about an axis substantially parallel to the said implant.
The means by which the displacement of the said movable element by the movement of the deformable element transforms this movement into a movement of rotation of the said other end, and of the fixing or anchoring means which it supports, can be a means combining a screw and a nut in such a way that the movement of translation of the one provokes a movement of rotation of the other.
In a particular embodiment, the deformable element is interposed between the two end pieces, one of which is capable of turning, in such a way that the deformation of the deformable element entrains at one and the same time a rotation and a translation of one of the end elements, and thus of the anchoring means which it bears, relative to the other end piece, translating into a helical movement of one of the end pieces relative to the other.
In another embodiment, the two end pieces can be secured to one another in such a way as to remain spaced apart by an invariable distance, the movable element then being interposed between this assembly of end elements and the means for transforming the deformation of the movable element into a rotation of one of the end elements relative to the other.
In another embodiment, it is the deformable element itself which is constructed to deform in rotation, for example by using a deformable chamber with rotary piston, according to the well-known principles of hydraulic rotation.
Devices capable of rotation, such as have just been described, can be particularly useful in cases of severe scoliosis or serious degenerative destabilization of the spine. In these cases, it will for example be possible to fix two devices according to the invention on either side of the posterior process of the vertebra, between two vertebral levels, and to provoke rotation between the two anchoring points of one of the two devices, or a rotation combined with a longitudinal displacement, the other device then being capable of a complementary movement of geometric adaptation of the displacements imposed by the first one.
All kinds of complex nonrectilinear displacements can be obtained by means of the intervention, for example by subjecting the displacement of an anchoring means, or of an end piece, to a cam or slide or other curved guide.
The implant consisting of a device according to the invention will preferably have an external shape suitably adapted to the physical environment in which it is located. For example, in particular for vertebral implants, it will be advantageous to give each of the two ends a streamlined shape so as not to disturb the adjacent tissues, especially since, by virtue of the implants according to the invention, it is possible to achieve a functional improvement which should involve the muscles and ligaments, in contrast to arthrodeses which cause their atrophy.
This streamlined shape can comprise an envelope, which is preferably deformable and is applied around the implant, and of which the two ends which having the fixing means for the anchoring means emerge from the envelope, the latter containing the various other components of the implant. The free internal volume in this envelope can preferably serve as a low-pressure liquid reservoir. The implant preferably includes, inside this envelope, the movable element which can be a mechanical motor or preferably a hydraulic motor, for example a hydraulic bellows, the interior of which is connected via a low-pressure valve to the low-pressure volume formed in the envelope.
Preferably, the interior of the envelope also includes a high-pressure reservoir, preferably a bellows, and, again preferably, a differential deformable element for sending liquid at very high pressure into the high-pressure reservoir, the high-pressure reservoir being connected to the moveable element likewise via a high-pressure valve, the high-pressure valve and the low-pressure valve preferably being relatively spaced apart from one another in order to easily permit a selective control by external control means, such as, for example, magnets.
However, in another embodiment, particularly when a succession of individual implants is provided at various levels of the spine, it is also possible to provide a single high-pressure reservoir and/or a single recharging means for recharging the high-pressure reservoirs, which is situated away from the various individual implants and is connected to these by inextensible conduits.
The high-pressure reservoir can advantageously be designed to maintain the liquid which it contains at high pressure, even when significant quantities of this liquid are sent to the motor means of the implant, provoking a substantial reduction in the volume of liquid. This can be effected, for example, by designing the high-pressure reservoir in the form of an elastically deformable reservoir of great stiffness, for example a metal bellows of great stiffness, which is expanded when it contains the liquid at high pressure, this bellows tending to retract in order to maintain the high pressure during a substantial part of its retraction travel. Alternatively, or in combination with such a bellows, it is also possible, in order to maintain the high value of pressure in the reservoir, to provide an energy accumulator in the form of a cell with an elastically deformable wall which is compressed, thus reduced in volume, when the high-pressure liquid is introduced into the high-pressure reservoir, and which relaxes elastically while at the same time maintaining a high pressure when liquid is withdrawn from the high-pressure reservoir. This energy accumulator is preferably in the form of a deformable capsule which can, for example, comprise in its interior an easily deformable substance or a gas, but which particularly preferably has a substantial vacuum so as to eliminate any risk of escape of gas.
The invention also provides for a skeletal implant of the type to be used to connect at least two elements of a skeleton, wherein the skeletal implant comprises a first part adapted to be connected to at least one of the at least two elements of the skeleton, a second part adapted to be connected to another of the at least two elements of the skeleton, a variable volume element adapted to move the first and second parts with respect to each other, a high-pressure chamber supplying fluid to the variable volume element a low-pressure chamber receiving fluid from the variable volume element and a recharging variable volume element is adapted to communicate with the high-pressure chamber and the low-pressure chamber.
The implant may further comprise another variable volume element disposed in the high-pressure chamber.
The implant may further comprise a high-pressure valve allowing fluid to enter the variable volume element from the high-pressure chamber.
The low-pressure chamber may comprise a deformable impermeable sleeve.
The implant may further comprise a low-pressure valve allowing fluid to exit the variable volume element and enter the low-pressure chamber.
The implant may further comprise a third part having one end coupled to the first part and another end disposed between the variable volume element and the second part.
The variable volume element may comprise one end coupled to the first part and another end coupled to a third part.
The implant may further comprise a third part having a threaded opening which engages a threaded portion of the second part.
The recharging variable volume element may comprise one end that is coupled to a third part and another end that is coupled to the first part. The second part may be rotatably coupled to at least one of the variable volume element and the third part.
The implant may further comprise a sealed bellows disposed in the high-pressure chamber.
The recharging variable volume element may be a metal bellows having one end coupled to the first part and another end coupled to a third part.
The implant may further comprise a sleeve defining a variable volume of the low-pressure chamber.
The implant may further comprise a high-pressure conduit connecting the variable volume element to the high-pressure chamber.
The variable volume element may comprise a metal bellows. At least one of the first part and the second part may comprise an opening which is adapted to receive a connecting member, whereby the connecting member connects the first or second part to one of the at least two elements of the skeleton.
The invention also provides for a skeletal implant of the type to be used to connect at least two elements of a skeleton, wherein the skeletal implant comprises a first part adapted to be connected to at least one of the at least two elements of the skeleton, a second part adapted to be connected to another of the at least two elements of the skeleton, a variable volume element having a first end coupled to the first part and a second end, the variable volume element being adapted to move the first and second parts away from each other, a third part having a first end coupled to the first part and a second end coupled to the second end of the variable volume element, a high-pressure chamber supplying fluid to the variable volume element, and a low-pressure chamber receiving fluid from the variable volume element.
The implant may further comprise a recharging variable volume element which includes a first end coupled to the first end of the third part and a second end coupled to the first part.
The recharging variable volume element may be adapted to communicate with at least one of the high-pressure chamber and the low-pressure chamber. The second part may be rotatably coupled to at least one of the variable volume element and the third part.
The implant may further comprise a high-pressure valve allowing fluid to enter the variable volume element from the high-pressure chamber.
The implant may further comprise a low-pressure valve allowing fluid to exit the variable volume element and enter the low-pressure chamber. At least one of the first part and the second part may comprise an opening which is adapted to receive a connecting member, whereby the connecting member connects the first or second part to one of the at least two elements of the skeleton.
The invention also provides for a skeletal implant of the type to be used to connect at least two elements of a skeleton, said implant comprising at least two parts, each of which is capable of being connected to one of said at least two elements, said at least two parts being movable with respect to each other, wherein there is provided, between said at least two parts at least one of a means authorizing a displacement between said at least to parts, from a starting position to a displaced position and a means exerting a force between said at least two elements of the skeleton. Said means is responsive to control means and comprises at least one variable volume element containing a fluid. Said control means comprises a high-pressure reservoir and a very high-pressure differential variable volume recharging element for sending fluid at high-pressure into said high-pressure reservoir. Said high-pressure reservoir is connected to said at least one variable volume element via a high-pressure valve. Said at least one variable volume element is connected to a low-pressure reservoir via a low-pressure valve. Said very high-pressure differential variable volume recharging element is connected to said low-pressure reservoir via another low-pressure valve. Said very high-pressure differential variable volume recharging element is responsive to displacements of corporal parts for recharging of said high-pressure reservoir with said fluid.
Said high-pressure reservoir may be designed to maintain said fluid contained therein at high pressure, even when significant quantities of said fluid are sent to said variable volume element, provoking a substantial reduction in a volume of said fluid, in order to maintain a high value of pressure in said high-pressure reservoir, and wherein said high-pressure reservoir contains an energy accumulator in the form of a cell having an elastically deformable wall, said energy accumulator being configured to assume a compressed and reduced volume state when fluid is introduced into said high-pressure reservoir, and being configured to assume an expanded state to maintain a high pressure when fluid is withdrawn from said high-pressure reservoir.
The invention also provides for a skeletal implant of the type to be used to connect at least two elements of a skeleton, said implant comprising at least two parts, each of which is capable of being connected to one of said at least two elements, said at least two parts being movable with respect to each other, wherein there is provided, between said at least two parts at least one of a means authorizing a displacement between said at least to parts from a starting position to a displaced position wherein the means comprises at least one variable volume element containing a fluid and a means exerting a force between said at least two elements of the skeleton. Said means is responsive to control means. Said control means comprises a high-pressure reservoir and a very high-pressure differential variable volume recharging element for sending fluid into said high-pressure reservoir. Said high-pressure reservoir is connected to said variable volume element via a high-pressure valve. Said variable volume element is connected to a low-pressure reservoir via a low-pressure valve. Said high-pressure valve and said low-pressure valve are relatively spaced apart from one another.